(A) Field of the Invention
The present invention relates to a capacitor structure of a semiconductor memory and method for preparing the same, and more particularly, to a capacitor structure having a multi-layered bottom electrode and method for preparing the same using deposition and electrochemical plating techniques.
(B) Description of the Related Art
A DRAM memory cell generally consists of a metal oxide semiconductor field effect transistor (MOSFET) and a capacitor, and the transistor includes a source electrode electrically connected to a bottom electrode of the capacitor. There are two types of capacitors: stacked capacitors and deep trench capacitors. The stacked capacitor is fabricated on the surface of a silicon substrate, while the deep trench capacitor is fabricated inside the silicon substrate.
FIG. 1 and FIG. 2 illustrate a method for preparing a stacked capacitor 22 according to the prior art. The method forms a semicrown-shaped bottom electrode 20′, and a dielectric layer 24 is then formed on the semicrown-shaped bottom electrode 20′, which is hollow. Subsequently, an upper electrode 26 is formed on the dielectric layer 24 to complete the stacked capacitor 22. The integrity of the dynamic random access memory increases rapidly with continuous improvements in the semiconductor fabrication process, but the lateral width of the capacitor must be decreased to achieve high integrity. However, decreasing the lateral width results in reduced size of the surface area, i.e., a reduced capacitance, which is proportional to the surface area.
To maintain or increase the capacitance of the capacitor, researchers increase the vertical height and decrease the lateral width of the capacitor to increase the size of the surface area of the capacitor, i.e., increase the aspect ratio of the capacitor to compensate for the decreased lateral width of the capacitor and achieve high integrity. However, achieving the objective of high integrity by increasing the aspect ratio of the capacitor creates an arduous problem, i.e., the hollow semicrown-shaped bottom electrode 20′, referring to FIG. 1, is likely to lean or even collapse due to insufficient mechanical supporting strength during the subsequent fabrication process.